1. Field of the Invention
This invention relates to the polymerization of hydroxyl-endblocked polydimethylsiloxane fluid and of polydiorganocyclosiloxane fluid in the presence of reinforcing filler using sulfuric acid or sulfonic acid as catalysts.
2. Description of the Prior Art
Marsden and Roedel, in U.S. Pat. No. 2,469,883, issued May 10, 1949, claim a process of preparing a solid, elastic, curable dimethylpolysiloxane by treating a liquid dimethylpolysiloxane with sulfuric acid or chlorosulfonic acid, then removing the acidic material after the solid, elastic product is formed. The product was further processed by mixing with filler and organic peroxide.
Buchner et al., in British Pat. No. 1,325,654, issued Aug. 8, 1973, disclose a process for manufacture of a mixture of high molecular weight linear organopolysiloxane with an acidic or neutral filler. They mix together a low molecular weight diorganocyclosiloxane, at least 0.05 percent of the weight of the siloxane of anhydrous perfluoroalkane sulfonic acid and filler. A low molecular weight triorganosiloxy-endblocked linear polydiorganosiloxane may also be present. After polymerization at a temperature below 50.degree. C., the mixture is neutralized with a basic substance. They teach that higher temperatures are disadvantageous in that polymerization only reaches a moderate degree, for example, up to an oil of about 1000 centipoise, if the initiator is neutralized at the temperature employed. They further teach that if the neutralization before cooling is omitted, an unusable gel is obtained.
Pike, in U.S. Pat. No. 3,078,255, issued Feb. 19, 1963, discloses a process for condensing hydroxyl-endblocked organosilicon compounds in the presence of a catalyst consisting of arylsulfonic acids or sulfonalkanoic acids, each containing no more than 18 carbon atoms.
Findlay and Weyenberg disclose in U.S. Pat. No. 3,294,725, issued Dec. 27, 1966, the polymerization of organosiloxanes in an aqueous medium using a surface active sulfonic acid as catalyst.